Theories of early language acquisition

What features of brain processing and neural development support linguistic development in young children? To what extent is the profile and timing of linguistic development in young children determined by a pre-ordained genetic programme? Does the environment play a crucial role in determining the patterns of change observed in children growing up? Recent experimental, neuroimaging and computational studies of developmental change in children promise to contribute to a deeper understanding of how the brain becomes wired up for language. In this review, the muttidisciplinary perspectives of cognitive neuroscience, experimental psycholinguistics and neural network modelling are brought to bear on four distinct areas in the study of language acquisition: early speech perception, word recognition, word learning and the acquisition of grammatical inflections. It is suggested that each area demonstrates how linguistic development can be driven by the interaction of general learning mechanisms, highly sensitive to particular statistical regularities in the input, with a richly structured environment which provides the necessary ingredients for the emergence of linguistic representations that support mature language processing. Similar epigenetic principles, guiding the emergence of linguistic structure, apply to all these domains, offering insights into phenomena ranging from the precocity of young infant's sensitivity to speech contrasts to the complexities of the problem facing the young child learning the arabic plural.     

U-shaped learning and frequency effects in a multi-layered perceptron: implications for child language acquisition

A three-layer back-propagation network is used to implement a pattern association task in which four types of mapping are learned. These mappings, which are considered analogous to those which characterize the relationship between the stem and past tense forms of English verbs, include arbitrary mappings, identity mappings, vowel changes, and additions of a suffix. The degree of correspondence between parallel distributed processing (PDP) models which learn mappings of this sort (e.g., Rumelhart & McClelland, 1986, 1987) and children's acquisition of inflectional morphology has recently been at issue in discussions of the applicability of PDP models to the study of human cognition and language (Pinker & Mehler, 1989; Bever, in press). In this paper, we explore the capacity of a network to learn these types of mappings, focusing on three major issues. First, we compare the performance of a single-layered perceptron similar to the one used by Rumelhart and McClelland with a multi-layered perceptron. The results suggest that it is unlikely that a single-layered perceptron is capable of finding an adequate solution to the problem of mapping stems and past tense forms in input configurations that are sufficiently analogous to English. Second, we explore the input conditions which determine learning in these networks. Several factors that characterize linguistic input are investigated: (a) the nature of the mapping performed by the network (arbitrary, suffixation, identity, and vowel change); (b) the competition effects that arise when the task demands simultaneous learning of distinct mapping types; (c) the role of the type and token frequency of verb stems; and (d) the influence of phonological subregularities in the irregular verbs. Each of these factors is shown to have selective consequences on both successful and erroneous performance in the network. Third, we outline several types of systems which could result in U-shaped acquisition, and discuss the ways in which learning in multi-layered networks can be seen to capture several characteristics of U-shaped learning in children. In general, these models provide information about the role of input in determining the kinds of errors that a network will produce, including the conditions under which rule-like behavior and U-shaped learning will and will not emerge. The results from all simulations are discussed in light of behavioral data on children's acquisition of the past tense and the validity of drawing conclusions about the acquisition of language from models of this sort.     

What’s in a name? Lexical knowledge drives infants’ visual preferences in the absence of referential input

Seventeen-month-old infants were presented with pairs of images, in silence or with the non-directive auditory stimulus ‘look!’. The images had been chosen so that one image depicted an item whose name was known to the infant, and the other image depicted an image whose name was not known to the infant. Infants looked longer at images for which they had names than at images for which they did not have names, despite the absence of any referential input. The experiment controlled for the familiarity of the objects depicted: in each trial, image pairs presented to infants had previously been judged by caregivers to be of roughly equal familiarity. From a theoretical perspective, the results indicate that objects with names are of intrinsic interest to the infant. The possible causal direction for this linkage is discussed and it is concluded that the results are consistent with Whorfian linguistic determinism, although other construals are possible. From a methodological perspective, the results have implications for the use of preferential looking as an index of early word comprehension.     

A computational and neuropsychological account of object-oriented behaviours in infancy

Infants under 7 months of age fail to reach behind an occluding screen to retrieve a desired toy even though they possess sufficient motor skills to do so. However, even by 3.5 months of age they show surprise if the solidity of the hidden toy is violated, suggesting that they know that the hidden toy still exists. We describe a connectionist model that learns to predict the position of objects and to initiate a response towards these objects. The model embodies the dual-route principle of object information processing characteristic of the cortex. One route develops a spatially invariant surface feature representation of the object whereas the other route develops a feature blind spatial–temporal representation of the object. The model provides an account of the developmental lag between infants’ knowledge of hidden objects and their ability to demonstrate that knowledge in an active retrieval task, in terms of the need to integrate information across multiple object representations using (associative) connectionist learning algorithms. Finally, the model predicts the presence of an early dissociation between infants’ ability to use surface features (e.g. colour) and spatial–temporal features (e.g. position) when reasoning about hidden objects. Evidence supporting this prediction has now been reported.     

Vowels in early words: an event-related potential study

Previous behavioural research suggests that infants possess phonologically detailed representations of the vowels and consonants in familiar words. These tasks examine infants' sensitivity to mispronunciations of a target label in the presence of a target and distracter image. Sensitivity to the mispronunciation may, therefore, be contaminated by the degree of mismatch between the distracter label and the heard mispronounced label. Event-related potential (ERP) studies allow investigation of infants' sensitivity to the relationship between a heard label (correct or mispronounced) and the referent alone using single picture trials. ERPs also provide information about the timing of lexico-phonological activation in infant word recognition. The current study examined 14-month-olds' sensitivity to vowel mispronunciations of familiar words using ERP data from single picture trials. Infants were presented with familiar images followed by a correct pronunciation of its label, a vowel mispronunciation or a phonologically unrelated non-word. The results support and extend previous behavioural findings that 14-month-olds are sensitive to mispronunciations of the vowels in familiar words using an ERP task. We suggest that the presence of pictorial context reinforces infants' sensitivity to mispronunciations of words, and that mispronunciation sensitivity may rely on infants accessing the cross-modal associations between word forms and their meanings.     

The role of novelty in early word learning

What mechanism implements the mutual exclusivity bias to map novel labels to objects without names? Prominent theoretical accounts of mutual exclusivity (e.g., Markman, 1989, 1990 ) propose that infants are guided by their knowledge of object names. However, the mutual exclusivity constraint could be implemented via monitoring of object novelty (see Merriman, Marazita, & Jarvis, 1995 ). We sought to discriminate between these contrasting explanations across two preferential looking experiments with 22‐month‐olds. In Experiment 1, infants viewed three objects: one name‐known, two name‐unknown. Of the two name‐unknown objects, one was novel, and the other had been previously familiarized. The infants responded to hearing a novel label by increasing attention only to the novel, name‐unknown object. In a second experiment in which the name‐known object was absent, a novel label increased infants’ attention to a novel object beyond baseline preference for novelty. The experiments provide clear evidence for a novelty‐based mechanism. However, differences in the time course of disambiguation across experiments suggest that novelty processing may be influenced by contextual factors.     

The Black Church,Values, and Secular Counseling: Implications for Counselor Education and Practice

There has been a recent increase in the amount of attention given in the counseling literature to addressing clients’ religion and spirituality. However, Black American churchgoers are rarely the target population in the discourse, and little is known about how the Black church shapes their views. This article provides information on values of the Black church and the church's influence on Black American churchgoers regarding secular counseling. Implications for counselor education and practice are discussed.     

Stochastic approaches to understanding dissociations in inflectional morphology

Computer modelling research has undermined the view that double dissociations in behaviour are sufficient to infer separability in the cognitive mechanisms underlying those behaviours. However, all these models employ multi-modal representational schemes, where functional specialisation of processing emerges from the training process. Targeted lesioning of different regions of functional specialisation leads to varied but predictable deficits in model performance. We argue that multi-modal representational schemes are not a necessary condition for the observation of double dissociations in an information processing system that shares resources across multiple tasks. Using a uni-modal representational system, we demonstrate that double dissociations may also result from stochastic processes. Lesioning experiments on a single-route, uni-modal connectionist model of regular and irregular noun and verb morphology confirm and extend earlier work demonstrating that selective impairment across tasks can result from damage to a distributed information processing system. A systematic investigation of the degree to which performance deteriorates across different inflectional classes reveals that simple and double dissociations can occur in this single-route, uni-modal model. An important prediction of the model is that double dissociations between regular and irregular inflection, resulting from stochastic processes should be extremely rare. However, they are particularly likely to occur when the researcher uses test batteries consisting of a small number of items. Given that cognitive neuropsychologists rarely provide details about the distribution of performance in a disordered population, it is concluded that a stochastic interpretation of double dissociations may have wider applicability than is normally supposed.